The Analysis And Research On Common-mode Voltage Suppression About The Motor Driven By PWM

Pulse width modulation(PWM)technology is widely used in converters.With the improvement of switching frequency and the increasing demand for suppressing control performance,some negative influences in converters attract people's attention.The motor driven by PWM inverters will have a common mode voltage in its neutral point.It will reduce the lifetime of the motor.At the same time,it will emit electromagnetic interference to other equipment.Therefore,the study of common-mode voltage is of great significance.The principle of PWM drive motor system about generating common-mode voltage in the neutral point of motor three-phase winding is studied in the paper.The causes,characteristics and transmission path of common-mode voltage are analyzed.The strategies of suppressing common-mode voltage have been researched.The hardware suppression method requires additional equipment,or topology changes require hardware redesign,which is more complicated.However,the software method has relatively low cost,and it can avoid the complexity of original system.So this issue is mainly studied from the software method in this paper.Two typical methods NZPWM and AZSPWM with zero-vector pulse width modulation are analyzed.According to the advantages and disadvantages of the two methods and their application range,a strategy of adopting different modulation method separately in different modulation regions is proposed.Aiming at the phenomenon that the amplitude increase of the common mode voltage caused by the dead zone when AZSPWM is used,a dead zone compensation method is proposed based on Extended Kalman filter.Considering that the random PWM strategy can extend the harmonic energy to a wide frequency range,several types of random PWM modulation strategies are introduced,and the functions of the random PWM are proved through simulation.The disadvantage is that although harmonic wave energy is dispersed and the maximum harmonic amplitude is decreased,but the fundamental amplitude and total harmonic distortion almost have no improvement.This paper proposes a genetic algorithm to optimize the random carrier frequency PWM method.The simulation results show that this method can effectively reduce the total harmonic distortion(THD)of output voltage and enhance Fundamental energy.To verify the correctness of the algorithm,taking the permanent magnet synchronous motor as an example,a model of PWM-driven motor system is built in MATLAB/Simulink.The control algorithm was written with S function to realize the new strategy of suppressing common mode voltage.A new type of suppression strategy without zero-vector was experimentally verified.